Prevalence of multiple sclerosis (MS) in two populations of the Kabardino-Balkaria Republic (Nalchik and Prokhladnensky region) was studied. In Nalchik, the prevalence of MS was 13.0 cases per 100 000 in 2006 and 13.7 cases - in 2010. It was lower among Circassians (8.0) compared to Slavs (31.3). The 5-year morbidity was low (0.15 per 100 000 population). In 2010, the prevalence of MS in Nalchik was 34.3 per 100 000. In the rural Prokhladnensky region with mainly Slav population, the prevalence was 11.0 cases per 100 000 in 2006 and 19.8 (all patients were Slavs) - in 2010. The morbidity was 1.76 for the period analyzed. At the same time, the prevalence of MS in the Slav population in 2010 was lower by a factor of 1.73 in the rural region compared to Nalchik (19.8 and 34.3, respectively). The higher prevalence of MS in Nalchik may be explained by adverse environmental factors increasing the risk of MS. A case-control study revealed the higher risk for people under 15 years old living very close to chemical and biological plants.